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Mechanisms are essentially used for converting motion from one form to another. Mechanical actuation systems mainly consist of mechanisms. If a number of rigid bodies are assembled together in such a way that the motion of one causes constrained or predictable motion of the others, it is called a mechanism. Thus, a mechanism transmits and modifies a motion.  The mechanism can be used for the following purposes: Transform linear motion into rotational motion (Example: IC engine) Transform a rotary motion into translating motion (Example: Cam and follower) Transform motion in one direction into another direction at right angles (Example: bevel gear or worm gear) Change (increase or decrease) and change the direction of the rotational speed of one drive to another (Example: gear trains) Figure 1. Linear to rotational motion transformation in IC engines Figure 2. Rotary to linear motion transformation in cam and follower Figure 3 Transformation of motion in one direction into another u...

In a modern camera using film, we can see automatic focusing and exposure facilities. The basic elements of the control system used in an automatic camera are body, lenses, and flash. Figure 1 depicts an automatic camera system. Figure 1: Components of an automatic camera Figure 2. Key components of an automatic camera and its block representation Depending upon the model selected, the required combination of aperture and shutter speed and focus are automatically taken care of by the camera.  A typical camera system comprises drives and sensors, interfaces for lenses, flash, and user.  Drives are required for film advance, rewind, shutter movement, focusing, zoom, etc.  The sensors are essentially used for sensing film speed, counters, focus, exposure, zoom, etc. Microprocessor systems for lenses, a user(s), and flash are incorporated for controlling various operations. Figure 3 Working of autofocus system of automatic camera The user is expected to feed information...

The washing machine is an example of a  sequential control system.  A system operating with sequential control is one where a number of preset operations are performed in sequence.  The control may be implemented as  event-based,  where the next action cannot be performed until the previous action is completed.  Another mode of sequential control is termed  "time-based",  where the operations are sequenced with respect to time. Example: An example of a time-based sequential control system is shown in the following Figure 1. The pump (fill valve) is switched ON for a particular time to fill enough water into the tank to fill it to approximately the correct level. Following this, the pump is switched OFF.   Figure 1: Time-based sequential control Among these two modes,  event-based control  is intrinsically  more reliable  than time-based control.  An example of an event-based sequential control syste...

Need of Accumulator The components of a hydraulic system require a continuous supply of pressurized fluid. For example, a hydraulic actuator gets the work done on the load by converting the energy of the fluid into mechanical energy.  In the absence of an accumulator, the hydraulic pump would be continuously running to cater to the need for valve operation. The pump will frequently start and stop, which affects the pump’s performance and its health.  A  hydraulic accumulator  is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure that is applied by an external source of mechanical energy. The accumulator stores energy which can be used in an emergency where there are no other means of power supply. It can be compared with the use of capacitors in electrical circuits.  Types of accumulators: Gas-charged (nitrogen usually) (Hydro-pneumatic accumulators) Spring-loaded Weigh...

The need for Pressure Relief Valve (PRV) A pressure relief valve (PRV) is one of the most important types of safety valves. These types of valves set a limit on the rise of pressure within a hydraulic line or system.  In normal operation, the valve is closed and no fluid passes through the PRV. But if the pressure in the line exceeds the limit, the valve opens to relieve the pressure.  This protects the expensive machines such as pumps, motors, and actuators from getting damaged due to extensive pressures.  Without a relief valve, pressure can continue to grow until another component fails and pressure is released. The need for Pressure Relief Valve (PRV) Types of Pressure Relief Valve Direct Acting PRV Pilot Operated PRV Direct Acting   Pressure Relief Valve Direct-acting PRV  is held closed by the direct force of a mechanical spring. The spring force holding the valve closed is opposed by the system hydraulic pressure.  The...

The key elements of a typical hydraulic system consist of the following components: Tank/ Reservoir:  The reservoir holds the hydraulic fluid (liquid petroleum oils and synthetic oils, usually oil) required for the hydraulic system. Filter:  Filters are used to remove any foreign particles so as keep the fluid system clean and efficient, as well as avoid damage to the actuator and valves. Motor-driven Pump:  The hydraulic pump is used to force the fluid from the reservoir to the rest of the hydraulic circuit by converting mechanical energy into hydraulic energy. The hydraulic pump which is the heart of the hydraulic system converts the mechanical energy int hydraulic energy. The mechanical energy is delivered to the pump via a prime mover such as an electric motor.   Pressure regulator:  The pressure regulator, as the name implies, maintains the pressure level of the hydraulic fluid. Whenever excess pressure level is generated, excess fluid is dope...

A system is a group of physical components combined to perform a specific function. A system has an input and produces output with the system being a black box that can perform some specific function. For example, an electric generator generates output power when a mechanical rotation is applied at the input.  Systems are classified into two main categories: Measurement systems:  Systems that measure required quantity are termed as "measurement systems". The key elements of a measurement system are: Sensor:  A sensor is a device that converts the physical quantity (quantity being measured) into a suitable electrical signal (signal related to measured quantity).  Signal conditioner:  The signal conditioner converts the output of the sensor into a suitable form for display. Display:  The display displays the value of a quantity that was being measured. Control system:  The basic objective of a control system is to regulate the value ...